Embodiments of the present invention relate to video test and measurement equipment, and more particularly to picture quality measurements for video.
Full reference video quality measurement and analysis performed by products, such as picture quality analyzers (PQA200, and PQA300) provided by Tektronix, Inc. of Beaverton, Oreg., use temporal registration. With temporal registration, each frame in a test video sequence is played at the same time the corresponding frame of the reference video sequence is played. With the proliferation of video formats and devices, and the associated proliferation in frame rates and temporal distortions or impairments, this prerequisite for the picture quality measurement and analysis preparation step has become more difficult to perform manually, and the automated methods of the prior art do not always work well.
In the prior art related to automatic methods for spatial distortion measurement, the methods suffer from one or more of the following shortcomings:                1) not robust over frame rate ratios other than 1.0;        2) do not give 1 to 1 of test and reference, given temporal distortions such as lost frames and frame freezes (both with an associated abrupt and locally static change in channel delay); or        3) do not work across frame resolution differences between reference and test, i.e., HD vs SD for example, and other spatial registration issues.        
An example of the prior art, as given in U.S. Pat. No. 6,751,360 entitled “Fast Video Temporal Misalignment Estimation” by Jiuhuai Lu and incorporated herein by reference, does not perform well, even if the video is identical but for one being a frame repeated version of the other. Methods that use correlation of frame differences as the primary or only means of frame distillation suffer from a “chopper” effect where frame differences are 0 for repeats, but not for non-repeats, resulting in correlations corresponding to FIG. 3. In FIG. 3, the frame repeats cause zero differences every other frame, corresponding to the dark horizontal lines and weak correlation for even the best match.
It would be desirable to have an automated method to measure temporal mapping, both linear and frame by frame, along with corresponding temporal impairments, such as freeze frames and blank frames, between the test video sequence and the reference video sequence. In particular, it is desired to have one method of measurement that is robust in the presence of digital compression artifacts, random noise, quantization error and other non-linear and linear distortions and interference. It is desired for this method to be adaptive in order to work without a priori knowledge of the video content, such as the Tektronix proprietary stripe added to the video signal currently for the PQA300; aspect ratio selected; DUT pixel clock; frame rates; or other indications of the general likely video parameters, including relative spatial mapping, horizontal or vertical scaling, offset (shift) or cropping.
Finally, it is desirable that the method has both good accuracy and computational efficiency. Computational efficiency refers to a relatively low level of processing for a given accuracy.